1. Field of the Invention
This invention relates to appliance systems used in orthodontic treatment.
2. Description of the Prior Art
The practice of orthodonitics involves the correction of dental irregularities and malocclusions by the application of forces to the teeth. The orthodontist applies corrective forces to the teeth requiring repositioning by attaching orthodontic appliances to them. These appliances are then connected to each other by a metal archwire. The orthodontist controls the amount and direction of the forces required to effect a repositioning of the teeth by selective bending of the archwire.
Current orthodontic treatment methods employing fixed orthodontic appliances are divided into two broad categories--the light wire method, of which the Begg method is one form, and rectangular wire (or edgewise) method, of which the straight wire method is one form.
The light wire method moves teeth by tipping and torquing the tooth into a new position. In the light wire method, an appliance or archwire receptacle, attached to a tooth, is connected to an archwire at what can be described as a point contact. Corrective force is applied to the tooth through the archwire, but due to the point contact connection between the archwire and the tooth, it is free to rotate and tip. This connection allows the tooth to move easily and large changes in tooth position are accomplished by the use of light forces. However, the freedom of tooth movement makes it difficult to accurately control positioning.
The rectangular wire method uses a more rigid system. A rectangular archwire is positioned in a rectangular slot in a tooth appliance or archwire receptacle. The tooth freedom of movement is limited by the rigid connection between the rectangular archwire and the rectangular receiving slot. A tooth so attached must move along or with the archwire and precise repositioning is possible. However, the rigid connection leads to large frictional forces; therefore, higher forces must be used to counteract the frictional forces and thereby move the tooth. Generally a longer treatment time is required for extensive tooth movement by this method than by the light wire method.
The straight wire technique is a modified rectangular wire system wherein the orthodontist first makes a model of the patient's dental arch. Using this model, he selects rectangular brackets having what he considers to be the proper amounts of torque and/or angulation to precisely reposition the teeth. These appliances are then positioned on the patient's teeth and a straight archwire is placed into the tooth brackets.
Generally speaking, orthodontists practicing in the eastern portion of the United States use light wire treatment systems while western orthordontists use some form of rectangular wire treatment. In our increasingly mobile society it is common for patients undergoing treatment to move from one part of the country to another. The patient may have difficulty obtaining the services of an orthodontist who is willing to continue treatment with the initially-chosen appliance system. Removal of the old system tooth brackets and replacement with those of another system is wasteful and extremely expensive.
Both the light wire and straight wire methods have advantages and disadvantages, as more fully discussed in "Begg and straight wire: A combination approach to treatment" by William Thompson, American Journal of Orthodontics, Vol. 79, No. 6, 591-608, June 1981. Generally the Begg light wire technique leads to rapid large movements of teeth with relatively little pain; however, it does not perform fine precision adjustments which are necessary for final tooth interdigitation. On the other hand, the straight wire technique leads to a relatively more accurate final alignment of teeth. However, the straight wire technique is more painful and requires longer treatment time to effect large tooth movements.
Often it is desirable to use Begg appliances for the large tooth movement portion of treatment and then switch to straight wire appliances to "fine tune" tooth adjustment during the final portion of treatment.
Various attempts have been made in the past to design orthodontic appliances that are capable of being utilized to effect both methods of treatment in order to gain the advantage inherent in each.
U.S. Pat. Nos. 3,163,933 and 3,178,822 describe combination one-piece orthodontic appliances having the capability of being used in either the light wire or rectangular wire method. These devices must be used from the beginning of treatment in order to switch from one appliance system to another.
U.S. Pat. No. 4,212,638 describes a combination light wire-rectangular wire orthodontic appliance system which provides the practictioner with means of employing both treatment methods without the necessity of changing tooth brackets during treatment. A bracket is provided which receives a light wire-type archwire. The archwire is secured to the bracket by means of a lock pin positioned in the bracket. An insert for holding rectangular straight wire-type archwires must be attached to the bracket by lock pins. The '638 patent requires the use of a standard "universal"-type tooth bracket to effect the conversion from one method to the other. Existing design brackets may not be used since they lack the necessary lock pin holes. Also, since the lock pins are extremely small, their insertion by an orthodontist presents quite a difficult procedure.
The converter disclosed in the '638 patent does not apply treatment corrective forces along relatively the same line of action for both treatment systems. For example, FIG. 3 shows the use of a light wire-type archwire. The light wire applies its force to the tooth to which it is attached slightly above the horizontal centerline of the bracket. FIG. 4 shows the converter and an attached straight wire-type archwire. The straight wire applies its force well below the horizontal centerline of the bracket.
Although of the above-noted references disclose conversion systems which constitute some form of universal tooth bracket useful only for the specific system disclosed, they cannot be used with common types of brackets presently used in either the straight or light wire systems. A patient who has only standard tooth brackets cannot utilize the advantages inherent in any of the above references. Thus, a patient who moves to another part of the country where his present treatment system is not in vogue may not convert to another system of treatment without removal of his or her old tooth brackets. Replacement of tooth brackets usually is extremely costly.
An orthodontist who already has an existing inventory of tooth archwire receptacles, including brackets, tubes, or sheaths designed for one specific treatment system cannot switch to the other form of treatment system during the course of treatment in order to utilize the advantages inherent in both systems. In order to use both systems for treatment, he must forego use of his present inventory of brackets and purchase an entirely new inventory of the universal brackets and inserts constructed in accordance with the teaching of one of the above references. Common business logic dictates that the patients, or their insurance companies, will eventually assume the cost necessary to acquire the new inventory of tooth brackets through higher orthodontist service fees.